Yes. There is Oxygen available on the train to Tibet. Tibet Train has two oxygen supplying systems on the Tibet train; The General oxygen outlet and the private oxygen outlet.
The General Oxygen outlet realizes oxygen for the entire cart. This system is Automate. It increases and decreases the oxygen output base on the amount of oxygen in the cart and elevation. To maintain the oxygen level, call the cabins on the train enclosed to prevent air leakage. The entire cabins are well-pressurised.
There is a private Oxygen outlet at all the beds on the train. You will also find the pipe to connect on it to breathe in the fresh air.
It is not guaranteed that you will not feel the effect of the High elevation sickness on the train or in Lhasa after arriving on the train journey. Thought Train to Tibet is pressurized, but it is not a much of a difference after arriving in Lhasa. But, we are sure it will help during your journey.
And for acclimatization in Tibet after arrival in Lhasa. Therefore, It is best to make your Tibet tour plans slow in the beginning to have a great Tibet travel experience.